The example you’ve picked favors the former screen. If you were changing the notetypes in the opposite direction (fluent->basic), the results would be reversed: the new screen would show only 4 fields, and the old screen would show lots of them.
The dropdowns are provided on the current notetype now so that an existing field can be mapped to multiple new fields, which makes it easier for users to duplicate fields and then later modify them. They’re on the left because it seemed more logical to have the old notetype on the left, but we could switch them so that it goes new ← old with the dropdowns on the right if people think that is more logical.
The existing notetype at the top is small so that maximum space is available for the new type, which is important on small screens. The rationale there being that the user probably knows what notetype the cards they selected are. On large screens it is unnecessarily small, and I’d be happy to accept a change that made it larger when width is less constrained.